When a carpet is installed, as for example a wall-to-wall carpet, it is stretched by the carpet installer with the aid of a carpet stretcher. The carpet is usually stretched to engage a tackless strip. The tackless strip is usually fixed to a floor about the perimeter of a room at a position closely spaced from the walls. If the carpet is not stretched adequately and uniformly, undesirable effects can occur. If a carpet is overstretched joins can separate leaving unsightly delineations between sections of carpet. If a carpet is understretched it can bubble and/or ruck becoming unsightly and dangerous.
The stretching characteristics of carpets are complex and variable. For example, tufted carpets should be stretched equally along their length and width, Axminster carpets have more stretch in the length, so they should be stretched lengthwise first, woven carpets should be stretched widthwise first, in most cases Velvet and Wilton weaves should be stretched widthwise first.
Carpet manufactures recommend that jute-backed tufted carpets be stretched "drum-tight". The amount of stretch needed for a polypropylene backed carpet is usually calculated as one and a half percent of the carpet length and width. The amount of stretching required is further complicated for jute-backed carpeting of lengths longer than 7 meters because the carpet tends to drag against the underlay and make the stretch "feel" tighter than it really is. In addition the amount of stretch required for a particular type of carpet varies between carpets produced by different manufacturers.
As a consequence a carpet installer is usually a highly experienced well practiced individual who is capable of making a qualitative judgement whether or not he has stretched a carpet properly. If the judgement is incorrect the carpet usually requires restretching. If the carpet is overstretched and begins to contract after settling the carpet in question might have to be replaced at the expense of the carpet installer
There has been little attempt in the past to provide a carpet stretcher which could be used in a variety of applications and also provide a quantitative measure of carpet tension. Prior art carpet stretchers were either limited to operation by highly skilled carpet installers who relied on their experience to "feel" the amount of stretch. Alternatively, prior art carpet stretchers were too complex in construction.
The first generic carpet stretcher used to a large degree was the "knee kicker". The knee kicker had an elongate body and employed a carpet engaging head at one end and a knee pad at the other end. The carpet installer applied an impulse via his knee to the knee pad whilst the head was engaged with the carpet. The installer had to make a qualitative judgement of the amount of stretch in a carpet and chronic knee injuries were frequent. Examples of knee kickers are given in U.S. Pat. Nos. 2,882,642 and 2,631,403.
To avoid injuries and the attendant compensation payments the "power stretcher" was developed. The power stretcher employs a carpet engaging head and a manually operable lever to extend the carpet engaging head and can be used to push from or pull to a stationary support. For example in U.S. Pat. Nos. 3,784,078 and 3,599,936 power stretchers are described which employ telescopic attachments. The telescopic attachments have a foot which in use is placed against a wall or other support near a fixed edge of a carpet being installed. The carpet engaging head is then engaged with the carpet adjacent an opposite edge of the carpet and the lever is pushed into its locked down position thereby extending the carpet engaging head a full length to stretch the carpet toward and into engagement with a fixed tackless strip. Some carpet installers recommend a plurality of full length extensions at each of a plurality of spaced locations along the carpet edge. Other installers use a larger number of smaller extensions at each point along an edge. The amount of stretch is determined as a qualitative judgement by the carpet installer. Another major problem with this form of power stretcher arises from the need to use telescopic attachments, particularly in large rooms, the set up time can be long and it is usually difficult to move the assembled stretcher.
Another power stretcher also employs a manually operated lever but does not use a telescopic attachment. As shown in U.S. Pat. Nos. 3,001,762, 3,980,274 and 3,963,216 a face plate can be used to fit in the space between the tackless strip and the wall. The tackless strip therefore provides a stationary support. On operation of the lever the carpet engaging head stretches the carpet to move the carpet edge toward and into engagement with the tackless strip.
In the aforementioned cases the lever operated power stretcher can only provide a qualitative measure of stretch. In addition the stretch is usually uneven across the carpet. The location of the lever and the requirement for manual operation necessitates the carpet installer to be on hand to operate the lever and does not permit the carpet installer to physically disturb remote areas of the carpet during stretching so as to more evenly distribute tension. It would be desirable for the carpet installer to walk over or scuff his feet on the carpet at locations remote from the carpet engaging head during the stretching operation. This would assist in distributing the tension. This is not possible with the aforementioned power stretchers.
The aforementioned carpet stretchers all operate on carpet where one edge is fixed, usually to a tackless strip. In the examples given a single carpet engaging head is employed. There are however, carpet stretchers which employ multiple heads. In U.S. Pat. Nos. 3,311,347 and 4,008,879 opposed heads are mounted on a ladder network and can be forced apart. The heads are usually located on opposite sides of a room to drive opposed carpet edges simultaneously onto opposed tackless strips. These arrangements provide more uniform tension than the single head stretcher because they operate on both edges. The ladder network can become very cumbersome in large rooms. These stretchers have found little application. Multiple head carpet stretchers are also used to force the edges of adjacent carpets together to form a join. One example is given in U.S. Pat. No. 4,394,004. This carpet stretcher employs two opposed heads one being a fixed head and the other a movable head. The movable head is located on a threaded stub which on rotation moves the movable toward or away from the fixed head. The rotation of the stub provides some quantitative measure of the applied tension However, the "feel" of the carpet installer still determines the limit of stretch for any one application. Once this is accomplished of course a corresponding number of rotations of the stub can be applied along the join.
Other attempts have been made to quantify the amount of stretch applied to a carpet but these have not found ready acceptance in the trade. For example in U.S. Pat. No. 1,929,837 a manually operated lever is used to rotate a pinion which meshes in a rack. The rack has a carpet engaging head at one end. While the amount of head extension can be regulated and reproduced along a carpet edge, the amount of stretch must still be determined by "feel".
A similar situation arises with power stretchers which have a variable extension mechanism to provide preselected extension of the carpet engaging head. In U.S. Pat. Nos. 3,693,936 and 3,917,225 a manually operated lever is operable at preselected extension of the carpet engaging head. The initial setting of the extension must be determined qualitatively by "feel".
In U.S. Pat. No. 3,311,347 a set of bathroom scales are incorporated in the carpet stretcher to measure compression force between opposed carpet engaging heads. While this arrangement provides a quantitative measure of the compression force between the two heads the carpet stretcher is cumbersome and the measuring means is not readily adaptable to a single head carpet stretcher.